Laser projection systems offer significant advantages over conventional lamp-based systems. For example, compared with conventional Xenon lamp projectors, laser projectors display videos and still images on to a projection screen with better contrast, colour gamut, uniformity, and brightness. In this way, cinema-goers are provided with an enhanced visual experience. However, one problem faced with front projection laser systems is the formation of laser speckle in the image observed by the viewer. Laser speckle is a consequence of the high spatial and temporal coherence of the laser light and occurs due to the interference of coherent laser light that is reflected from the projection screen. To a viewer looking at the front projection screen, the result is a granular image comprising bright and dark regions of light called a speckle pattern. The bright regions generally correspond to regions where the reflected light rays have constructively interfered, and the dark regions generally correspond to regions where the reflected light rays have de-constructively interfered. This speckle pattern varies depending on the viewing angle between the viewer and projection screen and its presence adds undesirable noise to the image.
The level of speckle can be quantified by the speckle contrast ratio. Most methods of speckle contrast reduction are based on generating different speckle patterns, so that the different speckle patterns average out in the eye of the viewer. Different speckle patterns can be produced by varying the illumination angle, polarisation and wavelength of the illuminating laser beam.